In hydraulic accumulators, it is necessary to prevent too much gas (typically air for low pressure accumulators or nitrogen for high pressure accumulators) from dissolving in the hydraulic fluid (oil) since if oil leaves the accumulator with air entrained in it, it can adversely affect the operation of the hydraulic components with which the accumulator is associated. This is especially so in atmospheric and pressure diffusers in the pulp and paper field. In such diffusers there typically is a high pressure accumulator which stores power for the sudden down stroking of screen components within the diffuser, and typically also includes a low pressure accumulator to absorb the sudden surge of oil from the down stroke so that it does not splash or slosh when it enters the atmospheric pressure oil reservoir. Conventionally, too much entrainment of gas in oil is accomplished by the provision of a boat or piston which floats on the top of the oil. However such boats are far from ideal, often sinking during use. When that happens it is necessary to turn off the accumulator, take it apart, and re-float the boat.
According to the present invention, a simple static, yet effective, structure is provided which prevents oil with dissolved gas from being discharged from the accumulator, and accomplishes this result in a relatively inexpensive manner. The apparatus according to the present invention may be utilized both for high pressure accumulators and for low pressure accumulators, and is less expensive and much more reliable than accumulators typically used commercially in atmospheric and pressure diffusers in the pulp and paper industry.
The most basic aspect of the present invention is to provide substantially laminar flow of the oil within the accumulator casing from between its contact with the gas and the outlet from the accumulator. In this way, in low pressure accumulators the liquid velocity is evened out across the cross-section of the accumulator so that there is no possibility of a central jet splashing against the roof of the accumulator entraining air, or otherwise entraining substantial quantities of gas therein. In the case of a high pressure accumulator, it is necessary for the gas to diffuse into the oil rather than being entrained by convection. Since diffusion is such a slow process and in view of the relatively long length of the laminar flow path, it is essentially impossible for oil with gas diffused therein to reach the outlet of the accumulator.
According to one aspect of the present invention a hydraulic accumulator is provided which comprises the casing, means providing at least one opening in the casing for the passage of oil into the casing and out of the casing, means for providing a gas pad acting on the oil within the casing, and means for providing laminar flow of oil from contact with the gas to the opening for passage of oil out of the casing so as to prevent entrainment of gas in oil that passes out of the casing. The laminar flow providing means may comprise a honeycomb, a plurality of solid bars with passageways between them, or a wide variety of other structures, but preferably comprises a plurality of tubes. Each tube has a substantially greater length than the largest cross-sectional dimension thereof, and the tubes are packed so that passageways defined therebetween also have a substantially greater length than the largest cross-sectional dimension thereof. Means are provided, such as a mounting flange welded to the outer tubes with inner tubes welded to the outer tubes, between the casing opening and the gas pad so that any oil passing from the gas pad to the opening and vice-versa must pass through the tubes or the passageways between them. The tubes typically are rigid and circular in cross-section.
It is most desirable that the casing be vertically oriented. The means providing at least one opening preferably comprises an inlet tube at the bottom of the casing, a baffle surrounding the inlet tube to prevent oil entering the casing from moving in a straight path upon initial entry into the casing, a perforated plate surrounding the inlet tube at the opening and leading from the casing to an outlet chamber, and an outlet tube leading from the outlet chamber to a component exterior of the casing.
Where the accumulator serves as a low pressure accumulator, with atmospheric air provided as the gas pad, the tubes provide a means for evening out the liquid velocity across a cross-section of the casing so that there is no central jet of oil that will splash against the roof. Where the accumulator is a high pressure accumulator, having a pressurized gas pad (typically nitrogen), the tubes provide means for ensuring that oil saturated with gas from contact with the gas pad does not mix with oil that actually leaves the accumulator through the opening.
The invention also relates to a diffuser for treating paper pulp including screen means and hydraulic means for reciprocating the screen means up and down. The hydraulic means comprises a high pressure accumulator which stores power for the sudden down stroking of the screen means, an atmospheric pressure oil reservoir, and a low pressure accumulator for absorbing the sudden surge of oil from the down stroke so that it does not splash when it enters the atmospheric pressure oil reservoir. At least one of the accumulators comprises a casing, means defining at least one opening adjacent one end of the casing for oil to enter and leave the casing, a gas pad, and a plurality of rigid tubes packing the casing between the gas pad and the opening, each of the tubes having a significantly greater length than the largest cross-sectional dimension thereof.
It is the primary object of the present invention to provide a simple, inexpensive, and effective hydraulic accumulator, particularly for use in association with a diffuser. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.